Method of producing selenium rectifiers



Nov. 28, 1944. r o. SASLAW 2,363,555

-'METHOD OF PRODUCING SELENIUM RECTIFIERS Filed Aug. 21, 1943 'INVENTOR. 0770 6,464 AW CHRBO/Y DIOXIDE Patented Nov. 28, 1944- METHOD OF Otto Saslaw. Lyndhurst,v

eral Telephone and N. 1,, assignor to Fed- Radio Corporation, New

York, N. Y., a corporation ofDelaware Application August 21, 1943, Serial No. 499,526

4 Claims. (or. 175-366) This invention relates to a method of making selenium rectifiers.

A selenium rectifier is generally made by uniting a layer of selenium with a metallic base plate,

a converting the selenium layer to the crystalline form by heat'treatment, forming on the selenium a blocking layer which is responsible for the rectifying action, applying a counter-electrode and finally electro-forming. The blocking layer may be formed by depositing on the selenium layer in the presence of moisture a thin film of selenium dioxide, for example by vaporizing the dioxide and allowing it to condense on the selenium sur face.

An important object of the invention is to improve a blocking layer of this type, and more specifically to decrease the reverse current characteristic of the rectifier without materially affecting its forward conductivity. It has been found that this can be done by depositing the sele um dioxide in an atmosphere of carbon di-- oxide and moisture on the selenium surface, prior to the application of the counter-electrode. The

gas, vapor and selenium .dioxid.. appear to. cooperate to give an enhanced blocking effect. It has also been found that theblocking layer can be further improved if the electro-formationis carried out in the presence of CO2 and moisture. Other objects and advantages will appear from the following detailed description and the attached drawing in which;

Fig. 1 is a diagram illustrating a process embodying a specific form of the invention, and

Fig. 2 is a fragmentary diagram illustrating a process for the electro-forming of a selenium rectifler.

According to a specific embodiment of the invention, the process may be conveniently carried out by allowing carbon. dioxide gas which has bubbled through hot water to contact the selenium surface and at the same time condensing on said surface fumes of selenium dioxide which has been heated to or above its perature.

Referring to Fig. 1, which illustrates this embodiment, l represents a tank of compressed C02 gas which discharges through a pipe 2 into the lower part of a water tank 3 suitably heated as by steam coils 4 and having a gas outlet pipe 5 connected to the tank above the surface of the water and discharging into a hood 6. An assembly of rectifiers 1 to be fumed is suspended in hood 8 through an opening in the hood, as by an arm 8 attached to a handle 9 by which said assembly can be moved into or out of the hood enclosure. An electric furnace III for heating .a crucible ll containing selenium dioxide is located in the lower part of hood 6 in position for ef-' fective fuming of the lower surfaces of disks 1.

When the apparatus is in operation, the valve l2 of the tank I is opened to allow C02 gas to flow into the pipe 2, thence into the bottom of the ,water tank 3 which is conveniently kept at a evaporating temshould be above 50%.

temperature of -95- C., from which the gas emerges at the top carrying moisture, passing through the overhead pipe 5 into the hood 6 where the wet gas envelops the assembly of rectifiers arranged with'their selenium surfaces exposed. At the same time, or shortly prior or subsequent thereto, the crucible H containing the selenium dioxide is heated to a temperature of approximately 400-500 C. to volatilize the oxide and cause it tobe deposited on. the free selenium surfaces.

After the selenium elements have taken up the required amounts of selenium dioxide, moisture and C02, they are removed from hood 6 and each is provided with a metallic counter-electrode, as by spraying. It is desirable that this be done promptly inasmuch'as it has been found that better rectifiers are produced when the counterelectrode is applied soon after deposition of the materials than when a long period of time is allowed to intervene. The delay should not exceed 30 seconds, and preferably is not more than 5 seconds.

At this stage the rectifiers are electro-formed by applying a rectified alternating current voltage for several hours in the direction of reverse current flow. An arrangement for this purpose is diagrammatically indicated in Fig. 2, 11]. which the negative terminal of the source is connected. to the metallic base plate is of the rectifier and the positive terminal is connected to the counterelectrode [4. Thedisks 1 during this operation are enclosed in a chamber l6 containing 002 and moisture, which may be introduced from tank 3 through pipe ll, the arrangement being such that the electro-forming step is carried out in an at mosphere of CO2 and moisture.

is used at a pressure of from 1 to 20 pounds per square inch gauge pressure, and preferably approximately 5 pounds. The room humidity Although the process has been described with particular reference'to a preferred embodiment involving the deposition of the selenium dioxide film on the selenium layer by means of vaporization and condensation of the oxide on said selenium layer, the invention is not limited to this method of depositing the oxide, and any other convenient method may be used for this purpose. The method of introducing the moisture, while especially advantageous, is likewise disclosed by way of illustration rather than limitation.

What is claimed is:

1. In the manufacture of aselenium rectifier, the method of forming a blocking .layer which comprises depositing a thin film of selenium dioxide on the selenium layer of a unit comprising a layer of selenium joined to a base plate, subjecting said selenium layer to an atmosphere of carbon dioxide and mositure and applying -a counter-electrode to said selenium layer.

2. The method as set forth in claim 1 in which the selenium dioxide film is deposited on said Gil selenium layer'in the presence of the carbon dioxide and moisture.

3. In the manufacture of a selenium rectifier, the method which comprises vaporizing selenium dioxide, causing said vapors to condense on a selenium layer supported one. base plate, in an atmosphere of carbon dioxide and moisture and immediately applying a counter-electrode to said selenium layer. 5

\ 4. In the manufacture of a selenium rectifier,

the method which comprises vaporizing selenium dioxide, causing said vapors to condense on a selenium layer supported on a base plate, in an atmosphere of carbon dioxide and moisture, applying a counter-electrode to said selenium layer and finally electro-forming said rectifier in an atmosphere of carbon dioxide and moisture.

O'I'I'O SASLAW. 

